Abrasive article



Dec.- 8, 1959 A. MfsUGA 2,916,368

- ABRAsIvE ARTICLE Filed July 51, 195e United States Patent ABRASIVE ARTICLE Arthur M. Suga, Philadelphia, Pa., assignor to Simonds Abrasive Company, Philadelphia, Pa., a corporation of Pennsylvania Application July 31, 1956, Serial No. 601,287 14 Claims. (Cl. 51-307) The present invention relates to a novel abrasive body possessing improved properties; and more particularly, it relates to improved grinding wheels and other solid abrasive articles having a ceramic bond comprising a liuorinecontaining amphibole. According to a preferred form of the invention, there are provided grinding wheels exhibiting greatly enhanced grinding ratios having a ceramic bond formed from a prelired, glassy frit and a iluorinecontaining amphibole.

Abrasive bodies, that is dense, rigid structures, having abrading properties, such as grinding wheels and the like, are well known. ln such bodies abrasive grain is bound together to form a dense, rigid structure generally by means of a ceramic or resinoid bond. ln those abrasive articles having a ceramic bond, abrasive grain comprises the discontinuous phase bound in a continuous phase of the ceramic bond. The bond should hold the abrasive grain together in the wheel in such a Way that each particle of abrasive grain performs its cutting work efciently. For example, abrasive particles should be retained in the wheel until they become dull, and as they become dull, bonding material should break away, releasing the dull particles and exposing new sharp abrasive points. In order to obtain such efficient utilization of the particles of abrasive grain it is important that the abrasive grain be rmly bound by the particular ceramic bond employed, otherwise the abrasive particles may be dislodged from the abrasive article before their useful abrasive life has been utilized. In order to effect a tenacious hond between the abrasive grain and ceramic bond, it is essential that the bond substantially completely wetV the surface of the abrasive grain. During the maturing of many ceramic bonds, the surface of the abrasive grain may be destroyed as by oxidation, which is particularly true in the case of a carbide type abrasive, such as silicon carbon, resulting in an unclean surface which is not easily wetted by the ceramic bond.

In `abrasive bodies, the bond material acts as a tool post to hold abrasive grain in the wheel. When the amount of bond is increased, the size of the posts connecting each abrasive grain to adjoining grains is increased accordingly. The amount of bonding material determines the hardness or softness of the grinding wheel, since the abrasive grain remains the same in both strength and grade. One measure of the hardness of abrasive articles, such as grinding wheels, may be expressed in terms of grinding ratio, i.e., the relationship between material removed to wheel wear. rl`his measure of hardness is indicated by the expression:

wherein M is the amount of material removed per unit time, and W is wheel wear measured in loss of weight of 'the wheel per unit of time.

The varying of the hardness or the softness of an abrasive body by increasing or decreasing the amount of meramic bonding agent present has distinct disadvantages. As the quantity of vitreous bond is decreased to provide a softer grinding wheel, the mechanical strength of the grinding wheel is decreased since, as previously mentioned, the size of the posts connecting abrasive grain to the adjoining grain is also decreased. Thus, a soft wheel, that is one having a low grinding ratio, also may be mechanically weak and willbe subject to fracture more easily than a hard wheel.

As stated previously, the bond should hold the abrasive grain together in the wheel in such a way that each particle performs its cutting work efliciently. Unfortunately, an abrasive body containing a proper amount of ceramic bond to provide the abrasive articles with the desired hardness or softness, may not hold the abrasive grain for such a period of time as to permit each particle to perform efficient cutting. This is so since the size of the posts connecting the abrasive grain vary with the quantity of bond present, so that the particles may break away from the abrasive body at a time when the abrasive particles still present sharp cutting surfaces, or the par-l ticles may be retained for too long a time so that they remain in the wheel after they have become dull, thereby preventing exposure of new sharp abrasive points.

It is the principal object of this invention to provide improved abrasive bodies having a novel ceramic bond comprising a liuorine-containing amphibole.

It is a further object of this invention to provide abra-` sive bodies of various degrees of hardness having sub@ stantially uniformly high mechanical strength.

Another object of this invention is the provision of a grinding Wheel having a ceramic bond comprising a fluorine-containing amphibole, which bond tightly binds the abrasive grain so that each abrasive particle is not released from the bond until its useful grinding life has expired.

Still another object of thisinvention is to provide a grinding wheel having a ceramic bond formed from a glassy frit and a fluorine-containing amphibole, which bond tightly binds the abrasive grain so that each abrasive particle is not released from the bond until its useful grinding life has expired.

A further object of this invention is the provision of grinding wheels having a ceramic bond formed from a prered, glassy frit and a fluorine-containing amphibole in which the hardness of the wheels may be varied without varying the quantity of bond, thereby maintaining a high degree of mechanical strength in the grinding wheels.

A still further object of this invention is the provision of abrasive bodies having a ceramic bond which do not suffer from the disadvantages of the prior discussed abrasive articles having a ceramic bond.

Further objects will become apparent from a consideration of the following specification and claims. v

The abrasive body of the present invention comprises abrasive grain bonded in a ceramic bond comprising a ilumine-containing amphibole which may be selected from the group consisting of fluoro-hornblende, iiuoro-cummingtonite, iluoro-soda amphibol'es and mixtures thereof. A preferred uorine-containing amphibole is a fluorosoda amphibole having a sintering temperature below about l750 F.

According to a preferred embodiment, the abrasive body of the present invention comprises abrasive grain bonded in a ceramic bond formed of a fused glassy frit and a ilumine-containing amphibole, the glassy frit having a fusing temperature below the sintering temperature of the amphibole. The preferred prered, glassy frit of the instant invention is a boro-silicate frit containing from about to about 40%, by weight, of boron trioxide.

The desirability of having a bond hold the abrasive grain at the grinding surface in such a way that each particle performs its cutting work elciently, i.e., the abrasive particles are retained in the bond until their useful abrasive life is exhausted, at which time they are permitted to break away from the bond to expose new sharp abrasive points has been discussed previously. It was found that the ceramic bond of the instant invention comprising a ilumine-containing amphibole tenaciously holds on to the abrasive grain to permit it to exert its fullest grinding action before being released from the abrasive article. It appears that the fluorine in the amphibole employed in the abrasive articles of this invention cleans the surfaces of the abrasive grain so that the ceramic bond may adhere more tenaciously to the grains which are ordinarily diicult to wet with bonding agent. The amount of fluorine needed to clean the surfaces of the abrasive particles is extremely small; however, the the time of release of free fluorine by the amphibole for this purpose appears to be of great importance. It is believed that at the sintering temperature of the amphibole, fluorine is released to clean the surfaces of the abrasive grain, at which time the abrasive grain is immediately wet by the sintered amphibole alone or, in accordance with a preferred form of the invention, by the amphibole and fused frit. If the fluorine is made available at a lower temperature, other volatile constituents, which volatilize subsequent to uorine, may again contaminate the particle surfaces which have been cleaned by uorine, thereby destroying the cleaning effect of the uorine and presenting a surface which is no longer easily wettable by the ceramic bond. On the other hand, if uorine is made available only at temperatures above the amphibole sintering temperature, luorine for cleaning abrasive particle surfaces will be released at temperatures which may cause decomposition of the amphibole. If attempts are made to add tluorine in chemically combined form by means of other compounds, as for example cryolite, obtaining the desired result is extremely diicult because of the great diiculty in determining the amount of fluorine compound to be employed and the manner of its addition.

It was further discovered that abrasive articles possessing a number of very desirable, yet unexpected, properties may be obtained by the provision of a ceramic bond formed from a prered, glassy frit and a iluorinecontaining amphibole, the glassy frit having a fusing temperature below the sintering temperature of the amphibole. As discussed previously, in varying the hardness of an abrasive body having a ceramic bond, such as a grinding wheel, it has been a practice to vary the quantity of bond. For example, in order to form a soft grinding wheel, it has been the practice to reduce the quantity of bond, which of course results in a reduction in the mechanical strength of the grinding wheel. According to the present invention, it has been found that when a fluorine-containing amphibole is employed in conjunction with a prefired, glassy frit which fuses below the sintering point of the amphibole to form a ceramic bond for a grinding wheel, the proportion of amphibole and glassy frit present may be varied over a wide range to provide grinding wheels of varying degrees of hardness. Yet, the mechanical strength of such grinding wheels is maintained at a substantially uniformly high level, for the total quantity of bond employed need not be varied and may be present in an amount which insures high mechanical strength. In addition to this property of the abrasive articles to maintain high mechanical strength through a wide range of grinding ratios, the abrasive articles having a bond according to this preferred form of invention, at certain particular glass-amphibole bond compositions, possess unexpectedly high grinding ratios, which ratios are 4 not obtained when a bond consisting essentially of amphibole or of the glass along is employed.

A further valuable property of the abrasive articles of this invention is that the articles can be machined with ordinary cutting tools, particularly where the bond essentially comprises a uorine-containing amphibole or contains a high proportion of fluorine-containing amphibole. Machinability of abrasive articles is extremely desirable since the machining thereof is often necessary to provide abrasive articles, as for example grinding wheels, with proper shape.

Still another advantage of the abrasive articles of this invention is that they can be produced by the hot press method, which method provides articles which are substantially non-porous and of greater density. Also, by means of the hot press method, the chance of fracturing abrasive articles during their manufacture is greatly reduced. Such fracture during manufacture is a serious problem, particularly where the abrasive grain is a costly material, such as diamonds, which, because of their great value, the economics of manufacturing abrasive articles with this abrasive grain requires its recovery from imperfectly manufactured articles. Thus, considerable advantage is to be gained by the instant invention in the preparation of diamond-containing abrasive articles, such as diamond wheels.

As stated previously, the amphiboles in the abrasive articles of the instant invention are fluorine-containing amphiboles, which preferably have a sintering temperature below about 1750 F. These uorine-containing amphiboles are known and are selected from the group consisting of nuoro-hornblende, fluoro-cummingtonite, uoro-soda amphiboles, and mixtures thereof. The amphiboles of the hornblende, cummingtonite and soda amphibole groups are described in Elements of Optical Mineralogy, Part II, by Winchell and Winchell. The amphiboles of the ceramic bond of this invention may be represented by the general formula:

in which R may be calcium, sodium, potassium, lithium, divalent iron, magnesium, divalent manganese, titanium, aluminum, trivalent iron, cobalt, nickel, and trivalent manganese; and X may be silicon, aluminum and boron. There rnust be at least 7 R-atoms per mole, and the sum of the valences of the R-atoms plus X-atoms equals 22. There may not be more than 3 univalent R-atoms per mole; not more than 5 divalent R-atoms per mole; not more than 4 trivalent R-atoms per mole; and not more than 3 tetravalent R-atoms per mole.

These amphiboles are members of the inosilicates, which are characterized by chains of indefinite length Vformed of SiO., tetrahedia linked together so that each tetrahedia shares two of its four oxygens with two different tetrahedia. Two such chains are linked into a double chain by alternate tetrahedia of one chain sharing a third oxygen of a tetrahedia of the other chain. Double chains are bonded to each other by the R-atoms of the above formula; particularly the alkali metal atoms. The orientation of the chains parallel to the C-crystallographic axis is responsible for the commonly presmatic or fibrous structure of the amphiboles, and also causes their presnlatic cleavage.

Typical of the fiuoro-hornblende group of amphiboles which may be employed in the ceramic bond of this invention are uoro-tremolite, CazMgSiO-ZEFZ and uoroferrotremolite, Ca2Fe5Si8O22F2, which arc the so called end members of the group, i.e., they are the end members of an isomorphic series in which divalent iron may replace one or more of the magnesium ions of the tremolite. Other members of the fluoro-hornblende group include uoro-pschermakite, Ca2l g2Al2Si6Al2O22F2, and lluorohastingsite, NaCa2Mg4AlSiGAl2O-22F2. Of the fluorocummingtonite group may be mentioned the end members, fluoro-kupfferite, MgqsiaOgzFeg and duoro-grunerite,

Fe7Si8O22F2, and the intermediate member uoroanthophyllite, (Mg, Fe)7Si8O22F2.

The preferred liuorine-containing amphiboles are the fluoro-soda amphiboles such as fluoro-glaucophane having the formulas: Na2Mg3Al2Si8O22F and uoro-riebeckite Na2Fe3++Fe2+++SiSO22F2; arfbedsonite, Na3(Fe++, Mg)4Fe+++Si8O22F2, and ickermannite,

A preferred uoro-soda amphibole is one having the general formula:

in which the manganese is in the trivalent state. This fluoro-soda amphibole has a sintering temperature Vof about 1750 F.

The uorine-containing amphiboles suitable for the purposes of this invention may be prepared by crystallization from melts of materials ultimately providing the desired amphiboles in proportions indicated by the particular amphibole formula. The melts should be formed -under conditions minimizing volatilization of fluorides as for example by covering the container for the melt. A reducing atmosphere is not employed. The iluorine-containing amphiboles employed in this invention are crystallized readily from a melt of such a composition. An amphibole having the composition Na2Mg3Mn2B2Si6O22F2 may be prepared by forming a melt by heating materials Isuch as Na2SiF6, MgO, MnCo3, B203 and Si02 to a temperature from about 1400 Ito l750 F., and crystallizing the amphibole from the melt. The fluorinecontaining amphibole, prepared for example by the method described above, may then be ground by conventional methods to a particle size suitable for forming the ceramic bond of the abrasive articles of this invention which should be generally less than about 100 mesh and preferably iiner than about 200 mesh.

The abrasive grain, from which the abrasive body is prepared, may be selected from a wide Variety of marterials well known in the art. The particular abrasive grain selected will, of course, depend upon the use intended for the abrasive body and upon the properties desired. Examples of abrasive grain are fused alumina, emery, corundum, diamond, zirconium oxide, siliceous materials, such as sand, flint and garnet, the Various carbides, such as silicon carbide, boron carbide, tungsten carbide, tantalum carbide and the like. The preferred abrasive grain is diamond, since as was indicated previously, the abrasive articles of this invention may be formed by the hot-press method, by which method the chances of fracture of the abrasive article during the manufacture are greatly reduced. Obviously, a minimum of manufacturing difculties are desirable where the abrasive grain em- -ployed is a costly material such as diamonds, and waste in -the form of imperfectly manufactured articles represents a prohibitive expense. The size of the abrasive grain may vary widely depending upon the properties desired in ,the nal product. The selection of a particular material for use as an abrasive grain, the particle size, distribution thereof, are considerations well known in the art and will present no problem to those skilled in the art. The

. proportion of abrasive grain in the product varies somewhat as is known to those skilled in the art.

With most types of abrasive grain, the grain may make up as low as about 40% of the nal abrasive product, but generally, it will range between about 60% and about 96%, by weight, of the product. Preferably, the abrasive grain makes up between about 75% and about 90% of the product. Where the abrasive grain comprises dia- `monds, because of their great cost, the abrasive grain preferably makes up between about 10% and about 25%, -by weight, of the final product. The remainder of the product comprises ceramic bond, and incertain instances, iiller material hereinafter described.

As mentioned heretofore, the abrasive articles of this invention comprise abrasive grain, ceramic bond, comprising a uorine-containing amphibole, and according to a preferred form of this invention, a bond comprising a preferred fused glassy frit, i.e. a glass, and a uorinecontaining amphibole, and in certain instances also a ller material. Thus, in the abrasive articles of this invention, the ceramic bond may make up all of that portion of the product which is not abrasive grain, i.e., with most abrasive grain up to about 60% of the nal product, and when the abrasive grain comprises diamonds, up to about of the product. Generally, with most types of `abrasive grain, the ceramic bond will comprise between about 4% and about 40%, and preferably between 10% and 25%, by weight, of the nal product. If the abrasive grain comprises diamonds, the ceramic bond preferably comprises between about 75 and 90%, by weight, of the iinal product.

The bond of the abrasive articles of this invention may essentially comprise a fluorine-containing amphibole. However, according to a preferred form of the invention, the bond of the abrasive body will comprise a glass phase and a phase consisting of a uorine-containing amphibole. As mentioned before, the latter bond may be employed to form grinding wheels of various degrees of hardness merely by changing the relative proportions of glass and amphibole in the bond. The mechanical strength of grinding wheels employing such a bond does not vary to any significant degree as the bond composition is varied since the amount of bond employed need not be varied but may be maintained at that amount which provides the necessary mechanical strength which is controlled for the most part by safety regulations. v In addition to the above advantageous features of the abrasive articles of this invention, it was found that at certain particular bond compositions formed of glass and fluorine-containing amphibole, unexpectedly high grinding ratios are obtained. This additional advantage of the abrasive bodies of the instant invention is best illustrated by reference to the drawing wherein value's of grinding ratios, i.e., M/ W for a diamond wheel are plotted against bond compositions. The curve, the method by which the valves through which it passes were obtained being more' fully described hereinafter, has a ielatively flat area at bond compositions containing less than Vabout 45%, and more than about 65%, by weight, of amphibole. With ceramic bonds having between about 45% and about 65%, and particularly between about 50% and 60%, by weight of amphibole, the remainder of the bond consisting essentially of glassy frit, the curve rises steeply to a peak and approaches a grinding ratio of 450 with a bond containing about 55%, by weight, of a fluorine-containing amphibole. On the other hand, grinding ratios not exceeding about are obtained when the amount of amphibole in the bond is less than about 45% or more than about 65%, by weight, and grinding ratios of less than 50 are obtained with a bond consisting essentially of glass or amphibole. Accordingly, a preferred bond is one formed of a glass and from about 50% to about 60%, by weight of bond, of a fluorine-containing amphibole.

The glassy frit employed in forming the ceramic bond of the abrasive articles of this invention should have a fusing temperature which is below the sintering temperature of the fluorine-containing amphibole. This is necessary to insure that the fluorine of the amphibole will be released to clean the surfaces of the abrasive grain at the proper time. If the glassy frit fuses at a temperature greater than the temperature at which the amphibole sinters, the amphibole will melt, decompose and lose certain valuable physical properties which contribute to `the advantageous properties of the ultimate abrasive point than the sintering temperature of the amphibole, the sintering temperature of thevamphibole is reduced so that the abrasive articles of this invention may advantageously be formed by hot pressing methods employing moderate temperatures which temperatures do not adversely alter the desirable abrasive properties of the abrasive grain, as for example by causing diamonds to undergo graphitization.

The glass portion of the bond, in the form of a fused frit, comprises between about 45% to about 75%, by weight, of silica, SiO2, and from about to about 40%, by weigh, of boron trioxide, B203. The frit may also contain alumina, A1203, in amounts up to about 15%, an alkali and alkaline earth metal oxides in amounts up to about 10%. The boron trioxide acts as a uxing constituent, and together with alkaline earth metal oxides, such as magnesia and lime, with or without the addition, of minor amounts of alkali metal oxide fluxes, reduces the temperature at which the frit softens so that its fusing point is below the sintering temperature of the uorine-containing amphibole. The alumina ingredient is a more or less neutral material and has valuable properties, ywhich include the quality of reducing the reactivity of the bond toward abrasive grain, such as silica carbide. Since the alumina increases the viscosity of the fused glassy frit, amounts of alumina in excess of about should not be employed, since temperatures greater than the sintering temperature of the amphibole may be necessary in order to provide the fused glassy frit with the desired fluidity to wet the surfaces of the abrasive grain. A preferred frit from which the glass phase of the bond is prepared comprises from about 40% to about 60%, by weight, of silica, from about to about 35% of boron trioxide, from about 10% to about 15% of alumina, and from about 5% to about 15% of alkali and alkaline earth metal oxides and mixtures thereof.

The bond will generally include other ingredients which may be termed impurities. For example, titania, which is probably not detrimental up to several percent may be present in some of the ceramic bonds made in accordance with this invention. However, it may be considered a relatively inert ingredient. Another impurtiy which is usually present, simply because it is practically impossible to eliminate all of it, it iron oxide, Fe203, which is more or less of a iiux. If all of the iron oxide could be eliminated, the invention could well be carried out without its presence, but on the other hand, it is believed that even as much as about 2% might, in some cases, be present without producing detrimental elects.

The composition, in the form of a frit, having the above-described chemical composition, may be prepared in accordance with conventional practice. As is well known, in preparing the frit, compounds ultimately providing the above-described oxide analysis, in the present case providing the above-described oxide analysis, are mixed together in ne particle size and melted, and the molten mass quickly cooled, by water-quenching and dried. With respect to the compounds employed, such compounds are well known in the art, and the provision of the above described chemical analysis will present no problem to those skilled in the ceramic art. Thus, the silica may be provided, for example, by quartz, sand or the like; boron trioxide, B203, may be provided for example, by borates, such as sodium borate, for instance, borax, boric acid, and the like; the alumina, A1203, may be provided, for example, by aluminum metaor orthophosphate, aluminum hydroxide, or the free alumina itself may be used; alkaline earth metal oxides, for example, calcium oxide, CaO, may be provided in the form of unslaked lime or the like; alkali metal oxides, such as sodium oxide, NagO, may be provided, for example, by sodium carbonate, soda ash, sodium carbonate monohydrate, and phosphates, for instance, tetrasodium pyrophosphate, sodium tripolyphosphate, sodium hexametaphosphate, and borate's, for instance, borax and the likel Materials, in ne particle size, providing the desired chemical analysis upon melting thereof, are mixed together in accordance with the common practice and heated to an elevated temperature to provide a molten, pourable mass. The molten mass is then quickly chilled, such as by pouring it into a water bath, and such quick chilling causes the glass-like mass to fracture into small pieces. These small pieces are recovered and dried to provide the frit having the chemical analysis described above. The resulting frit may be too coarse for direct use in the ceramic bond, and may, therefore, be ground to the desired size in accordance with well known practice. The particle size of the glassy frit should be less than about mesh (U.S. Bureau of Standards) and preferably finer than about 200 mesh.

In addition to ceramic bond, the abrasive articles of this invention may have incorporated therein a filler material. Filler materials are substantially insoluble, inorganic materials which are capable of existing in discrete, finely-divided form, and are not fused at the bond maturing temperature. Examples of such materials are alumina and carbides such as silicon carbide, boron carbide, tungsten carbide, tantalum carbide, and the like. These filler materials, which are themselves abrasives, all fuse at temperatures above those required for maturing of the ceramic bond. Such ller materials generally should have a particle size of less than mesh, for example, from about 150 to 600 mesh, and preferably from about 300 to about 340 mesh. The particle size of the filler preferably is smaller than the particle size of the abrasive grain employed, particularly where the abrasive grain is diamond, in order to simplify separation of abrasive grain from ller upon reclaiming of abrasive grain by such well known methods as sieving. These fine-grain filler materials make the bond more resistant to wear, and since the filler is an abrasive which may be the same as the abrasive grain employed, it acts to equalize the coefficient of expansion and contraction with heat of the bond with respect to the abrasive grain. The preferred ller is a carbide filler, such as finelydivided silicon carbide.

Advantageously, the abrasive article of this invention may be formed by the hot press method, which method produces an abrasive article of greater density, and by which method the likelihood of fracture of the molded abrasive article is substantially reduced. The hot pressing technique employed in the manufacture of the abrasive article of the instant invention are those well known in the art, and comprises broadly forming a thorough mixture of abrasive grain, ground amphibole, ground prefired, glassy frit and filler, if any, placing the mixture in a graphite mold and subjecting the mixture in the mold to heat and pressure. Pressures up to about 1500 p.s.i. are generally employed with temperatures suficiently high to cause the amphibole to sinter. However, hot press temperatures should not greatly exceed the sintering temperature of the amphibole, otherwise, the amphibole may be decomposed. Temperatures employed generally range between about 1200 and l750 F.

In the abrasive articles of the present invention, the abrasive grain comprises the discontinuous phase and the ceramic bond comprises the continuous phase. This is the case where the ceramic bond essentially comprises a ilumine-containing amphibole, or according to a preferred form of the invention where the bond is formed from a preiired, glassy frit and a fluorine-containing amphibole. In the latter instance, it is believed that the fiuorine-containing amphibole and fused prered, glassy frit do not unite to form a single ceramic material, but rather retain their separate identity. For example, if the ceramic bond includes a high percentage of glass, as for example 80% glass, the fused glassy frit will comprise the continuous phase, and the amphibole will be distrib- Dted throughout the fused glassy frit in the form of discrete particles. On the other hand, if the proportion of amphibole present in the ccramic bond is substantially greater than that of the fused frit, the amphibole, upon sintering, will become the continuous phase with discrete particles of fused glassy frit dispersed throughout the amphibole. Regardless of the actual physical form of the ceramic bond, the ceramic bond of this invention produces the heretofore mentioned advantageous results.

Preparation of the product of this invention will be more clearly understood from a consideration of the following specific examples which are given for the purpose of illustration and are not intended to `limit the scope of this invention in any way.

EXAMPLE I The following materials are mixed together in a ball for about 60 minutes:

The Si02 is added in excess of its percentage composition to allow for a moisture loss of 21.6%. The ground mixture is placed in a f re clay Crucible having a silicon carbide lid and the mixture is heated at elevated temperatures for a period of about 9 hours under somewhat oxidizing conditions. During the rst hours of heating, the mixture is heated from room temperatures up to a temperature of about 1700 F., at which latter temperature the mixture is maintained during the last 4 hours of heating. During heating to the holding temperature of 1700 F., it is necessary to hold the temperature between the 3rd and 4th hour of heating at about 900l000 F. in order to melt the B203 (MP. 842 F.). After cooling, all the material is ground to ner than about 270 mesh in an electric mortar and pestle. The amphibole so produced is a fluoro-soda amphibole having the general formula:

Na2Mg3MD2+++B2Sl6O22F2 EXAMPLE II A 1/2" 0.D. x Ms" I.D. x 1A thick diamond grinding wheel is formed by hot pressing the following dry mixture of materials:

Percent by weight Prered, glassy frit, less than 200 mesh 25 Fuorine-containing amphibole of Example I 30 Diamonds, 100 to 140 mesh 25 Silicon carbide filler, less than 200 mesh 20 The prefired glassy frit has the following composition:

Percent by weight Silica, Si02 4448 Boric oxide, B203 28.88 Alumina, A1203 13.85 Magnesia, MgO 10.27 Lime, CaO 2.05 Titania, Ti02 0.80 Ferrie oxide, Fe203 0.25

is stripped from the moldl 10 the molding process are obtained by means of a thermocouple located in the mold shell.

The wheel is mounted on a steel mandrel and the wheel is driven at high speed by compressed air. The wheel is employed to grind a sample of tungsten carbide. A grinding ratio, M/ W, of 447:1 is obtained.

A number of diamond grinding wheels are made in the manner of Example 1I with a iluoro-soda amphibole, made in a manner similar to the method of Example I. However, the amount of nuoro-soda amphibole in .the ceramic bond is varied, a greater or lesser amount of silicon carbide filler being employed in the Wheel composition so as to maintain the total quantity of amphibole plus ller substantially constant. The amount of glassy frit is maintained constant with the exception that in one example ythe frit is entirely omitted, and in another where amphibole is omitted, the amount of frit is increased to 50% of the total wheel composition. The results of these examples are set forth in Table l below.

T able I Amphibole Glassy Dia- Filler, Maxi- (1 y vll" vfnpt- Si@ Wt Srlw iom Wt. Perwt. Percent of when Temp., M/W

cent of Percent F. Wheel of Bond Wheel 75 100 0 25 0 1, 750 15:1 50 66 25 25 0 1, 405 135:1 40 62 25 25 10 1, 520 152:1 40 62 25 25 10 l, 550 147: 1 35 58 25 25 l5 1, 550 204:1 30 55 25 25 20 1, 580 408:1 30 55 25 25 20 1, 610 423: 1 25 50 25 25 25 1, 555 174:1 20 44 25 25 30 l, 610 123:1 0 0 50 25 25 1, 355 63: 1

The data of Table I has been plotted to obtain the curve illustrated in the drawing and discussed previously. The curve clearly illustrates the unexpectedly high grinding ratios that can be obtained with a ceramic bond formed from a glassy frit and a fluorine-containing amphibole, in which bond the amphibole comprises from about 45% tto about 65%, and preferably from about 50% to about 60% by weight of the bond.

I claim:

1. An abrasive body comprising abrasive grain bonded in a ceramic bond consisting essentially of a fluorinecontaining amphibole and a borosilicate glass consisting essentially of from about 40% to about 60%, by weight, of silica, from about 20% to about 35% of boron trioxide, from about 10% to about 15% alumina, and from about 5% to about 15% of a material selected from the group consisting of alkali and alkaline earth metal oxides, and mixtures thereof, said amphibole and said glass comprising separate phases of said bond, and said amphibole phase comprising from about 45 -to about 65% by weight, of said bond.

2. An abrasive body comprising abrasive grain bonded in a ceramic bond consisting essentially of a uorinecontaining amphibole selected from the group consisting of a uoro-hornblende, a lluoro-cummingtonte, a uorosoda amphibole, and mixtures thereof, and a borosilicate glass consisting essentially of from about 40% to about 60%, by weight, of silica, fromabout 20% to about 35% of boron trioxide, from about 10% to about 15% alumina, and from about 5% to about 15% of a 'rnaterial selected from the group consisting of alkali and alkaline earth metal oxides, and mixtures thereof, said amphibole and said glass comprising separate phases of said bond, and said amphibole phase comprising from about 45% to about 65% of said bond.

3. An abrasive body comprising abrasive grain bonded in a ceramic bond consisting essentially of a uorinecontaining amphibole of the general formula:

and a borosilicate glass consisting essentially of about 45%, by weight, of silica, about 14% alumina, about 25% boron trioxide, about 2% calcium oxide and about magnesium oxide, said amphibole and said lglass comprising separate phases of said bond, and said amphibole phase comprising from about 45% to about 65% by weight, of said bond.

4. The product of claim 1 in which said uorine-containing amphibole comprises from about 50% to about 60%, by weight of said ceramic bond.

5. The product of claim 1 in which said uorine-containing amphibole has a sintering temperature below about 1750" F.

6. The product of claim 1 in which said abrasive grain comprises diamonds.

7. The product of claim 2 in which said uorinecontaining amphibole has a sintering temperature below about 1750 F.

8. The product of claim 2 in which said abrasive grain comprises diamonds.

9. The product of claim 2 in which said fluorinecontaining amphibole is a uoro-soda amphibole.

10. The product of claim 2 in which said uorine- 12 containing amphibole comprises from about 50% to about 60%, by weight of said ceramic bond.

11. The product of claim 9 in which said uorosoda amphibole has the 'general formula:

12. The product of claim 11 in which said abrasive grain comprises diamonds.

13. The product of claim 3 in which said uorinecontaining amphibole comprises from about 50% to about 60%, by weight of said ceramic bond.

14. The product of claim 3 in which said glass comprises about by weight, of said body, said amphibole comprises about said abrasive grain is diamonds and comprises about 25%, and the remainder of said body essentially comprises a finely-divided silicon carbide filler.

References Cited in the le of this patent UNITED STATES PATENTS 

1. AN ABRASIVE BODY COMPRISING ABRASIVE GRAIN BONDED IN A CERAMIC BOND CONSISTING ESSENTIALLY OF A FLUORINECONTAINING AMPHIBOLE AND A BOROSILICATE GLASS CONSISTING ESSENTIALLY OF FROM ABOUT 40% TO ABOUT 60%, BY WEIGHT, OF SILICA, FROM ABOUT 20% TO ABOUT 35% OF BORON TRIOXIDE, FROM ABOUT 10% TO ABOUT 15% ALUMINA, AND FROM ABOUT 5% TO ABOUT 15% OF A MATERIAL SELECTED FROM THE GROUP CONSISTING OF ALKALI AND ALKALINE EARTH METAL OXIDES, AND MIXTURES THEREOF, SAID AMPHIBOLE AND SAID GLASS COMPRISING SEPARATE PHASES OF SAID BOND, AND SAID AMPHIBOLE PHASE COMPRISING FROM ABOUT 45% TO ABOUT 65% BY WEIGHT, OF SAID BOND. 